Current viewpoints assume that manifestations of sickle cell disease result from the obstruction of capillary networks by abnormal erythrocytes during deoxygenation. Using a commercially available Laser Doppler Velocimeter (Med Pacific LD 5000) we propose to monitor non-invasively cutaneous blood flow in stable sickle cell patients under various conditions of steady state and perturbed flow. Additionally, since red cell deformability is a key factor in determining capillary flow we will monitor in vitro filtration rates of cells under various conditions.